THE NATURAL HISTORY SURVEY. 287 
b. Aperture expanded or bell-shaped. 
1. Both upper and lower surface forming a cone-shaped 
depression, the edge of the last whorl, above and be- 
low, bordered by a sharp carina................... bicarinatus 
2. 
Upper and lower surface on same plane, not form- 
ing a depression; all of the whorls visible aboveand 
two rounded whorls visible below. No carina. ..campanu/atus 
Fic, 95. 
Genitalia of PLANORBIS CORNEUS. (Bronn, Klassen und Ordnungen 
der Weichthiere, Malacozoa, taf. CIII, Fig. 10.) dh, ovisperm duct; gh, 
ovotestis; gal, albuminiparous gland; od, oviduct; p, penis; pr, prostate; 
rs, receptaculum seminis. 
B. Shell small, dextral. 
a. Periphery acutely keeled. 
1, Umbilicus narrow and rather deep 
REX ra stile Sicusih's hee exacutus 
b. Periphery rounded or obtusely keeled. 
1. Umbilicus shallow and broad. 
+Whorls well rounded, aperture ovate................. parvus 
+tWhorls angular, aperture deflected................ deflectus 
SusGENnus HELISOMA Swainson, 1840. 
“Shell ventricose, whorls angulated. Spire sunk below 
the body whorl.” ( Dall.) 
a ee Ce 
